The text of this background section is to prepare the reader for understanding practices described in this disclosure. The text is not presented with a consideration of whether it discloses prior art.
Multi-cylinder, reciprocating piston, internal combustion engines for automotive vehicles typically contain an oil circulation system for lubrication of valves, cylinder walls, pistons, connecting rods, cranking mechanisms, and the like. Generally, a predetermined quantity of lubricating oil (e.g., four to six quarts) is stored in bucket-like sump container attached to the engine below the cranking mechanism. When the engine is operating, an oil pumping mechanism, often driven off the engine, draws lubrication oil from the sump container and pumps it upwardly over all moving engine parts. The oil is drawn through an oil pick-up or inlet tube positioned below the surface of the sump oil. The oil flows in an oil circulation path, as intended and provided, over engine parts requiring lubrication. As it completes its flow, the oil drains downwardly back into the sump container. Typically, less than half of the stored volume of oil is in circulation at any moment of engine operation. In this way an adequate supply of oil is assured despite irregular motion of the vehicle, or leakage of the oil or burning of some of the oil as it is exposed on cylinder walls.
The oil is heated during engine operation, often to temperatures of about 90° C. to about 110° C. and at this temperature the oil has a viscosity and flow properties well suited for lubrication of engine surfaces. But when engine operation has ceased, the stored and now quiescent oil is cooled to the ambient temperature in which the vehicle is situated. Since this temperature may be well less than about 30° C., temperature-dependent properties of the oil are often less than desired for engine operation. So the oil may be relatively cold and viscous as its circulation is commenced immediately following an engine cold start. Sometimes vehicles intended for cold climates have special oil heaters located in the sump container for keeping the oil at a desired temperature between intermittent usages of the engine. Most vehicles do not have such an oil heater. But there is a need to reheat the circulating oil for better engine operation and less engine wear. A difficulty is that the total volume of oil is considerably larger than the amount being circulated and heated by the engine at any operating moment.